Thermal well-logging



Jun 27, 1944. L w L ETAL 2,352,247

THE I QMAL WELL-LOGGING Filed June 4; 1938 Patented June 27, 1944 THERMAL WELL-LOGGING Ludwig W. Blau and George E. Cannon, Houston,

tandard Oil Develo Ten, assignors to 8 Company, a corporation of Delaware pment Application June 4, 1938, Serial No. 211,726

1 sclaims.

The present invention is directed to a method and apparatus for studying and differentiating tween substrate traversedby a borehole. More particularly, the present invention resides in a method and apparatus for making thermal measurements in a borehole.

It has long been known that temperature increases with depth in a borehole, and that useful information concerning the nature of substrata traversed by the borehole can be obtained by making thermal measurements adjacent these substrate. In general, the procurement of this information has in the past been confined to the measurement of the temperature at various points along the borehole and to the measurement of the temperature diiierential between vertically spaced points in the borehole. The diiflculty with this method is that it gives no certain indication of the nature of the substrata traversed by the borehole since the vertical gradient may be due itive thermal data with regard to substrate traversed by a borehole are secured by measuring a value indicative of the thermal conductivity of the substrata traversed by the borehole, by measuring the horizontal gradient oi temperature in the borehole, and/or the heat absorptive properties of the substrata traversed by the borehole. These measurements may be made independently .or simultaneously and may be advantageously supplemented by the independent and simultaneous measurement, of the vertical gradient of temperature in the borehole.

Briefly, the method 01' the present invention consists in circulating the fluid which is ordinarily contained in a borehole so as to remove from the borehole such fluid as may have reached the stage of thermal equilibrium with the substrata, and replacing this fluid with fresh fluid which is, in general, at a temperature diflerent from the temperature any of the substrata, allowing suflicie'nt time 'to elapse for temperature changes to occur in the freshs fluid due to the heat contained in and the thermal conductivity the power necessary to temperature oi said source constant, or passing along borehole a "sour ce of heat supplied-i by 'a constant source of power and measuring'thetemperature' changes of said o l-heat g The nature and objects of th'e'priasentdnvention will 'be'morejfully underst q'rr mitne m1- lowing detaileddescription or the accompanying drawing in whicha Figure 1 is a'diagralnmatic illustration',partly in section, or an arrangementfsuitable for the measurement of the horizontal temperature gradient of the borehole fl\iid:;and I Figure 2is a 'sim ilar-illustration or anhrrangement which may be employedior simultaneously the heat absorpti'vity oithe borehole fluid. the horizbntal temperaturgradient of the fluid, and the vertical temperature .g'radient of the fluid.

Referring to Figure 1 in detail, numeral l designates the earth in which is a borehole I filled with a fluid, such as mud I. A body I of heat insulating material, such as Bakelite. is adapted to be lowered into the borehole on a cable, not shown. carrying conductors I. which are connected across a voltage measuring device 6 at the surface.

'Ihe'body I has a central passage! throughout its length which terminates inthe'lower end of the body in one Junction I or a thermocouple.

The lower end of 'e I is surrounded by a cylinder 0 or :small diameter which in turn is surrounded by an annular chamber II provided at its inner end with a laterally extending passage 5 ll connecting chamber II with the outside or body I. The outer wall or annular chamber II is coextensive in length with the cylinder- I and is provided at its lower edge with a second junction It oi a' thermocouple. Jimctions I and I2 40 are connected by an iron wire H, and are connected in series with the recording instrument 6 by conductors I. The itmctiom I-hnd it are exposed to the fluidin the borehole. There may be as manyiunctions it as arranged around the circumi'erenc'e of the lower-edge oi oi the various substrate, and than measuring the horizontal temperature gradient at successi've points in the borehole, and/or measuring the heat absorptivity of the fluid at successive points. In making the latter. measurements, one may proceed by passing a source of heat of constant temperature along the borehole and measuring body I, the voltage recorded being a iunction of the number or these Junctions.

As can be seen, the Junction I: will assume the temperature oi the fluid, adjacent the borehole wall while the Junction I will assume the temperature or the center oi the column oi fluid. The voltage recorded, therefore. will be a function of the temperature diflerential between the wall oi the borehole and the center of the column oi iiuid. This diirerential will depend upon the conductivity of the wall of the borehole. Sometimes the borehole will be provided with casing, but this will have a uniform conductivity throughout its length and will, therefore, have no efiect n the measurement of the horizontal gradient of temperature. As can be understood, if all of the substrata had the same conductivity, the temperature change would be the same throughout the length of the borehole, since, in general, the conductivity of the drilling fluid remains constant throughout the length of the borehole. Accordingly, variations in the potential created by the thermocouple can be attributed to the conductivity-of the substrate traversed by the borehole.

In practicing the method of the present invenand is'designated by numeral 25; Junctions 24 and 25 are connected by an iron wire 28 and are also connected by conductors 2'! too. voltas recording instrument at the surface. At the-sur- I face will be an instrument for recording the voltage created by thermocouples I and I2, an instrument for recording the voltage created by thermocouples 24 and 25, andan instrument for measuring the energylost from the heating coil l8. These instruments are conventional in the art and are designated collectively by numeral 2!.

The nature and objects of the present invention having been thus described and illustrated.

what is claimed as new and useful and is desired tion with the apparatus above described, the

cable carrying the body 4 is mounted on a drum at the surface in the conventional manner. The

body a is lowered throimh the borehole at a regulated constant speed. As the body 5 passes downwardly the drilling fluid in the borehole passes through annular passage 16 and passage ll thereby insuring that the junction 8'will follow the variations in temperature along the center of the borehole. The voltage measuring instrument is, preferably, of the recording type and is used in conjunction with a moving strip of photosensitive paper in the manner conventional in well-lo ging methodsl In the event that it is desired to observe and record simultaneously the heat absorptivity' of the substrata, the horizontal temperature gradient alone the borehole and the vertical temperature gradient along the borehole, an arrangement such as shown in Figure 2.may be employed.

In this arrangement the body M, containing the heating coil i8 and the thermostat II, is rigidly secured to the body 6 shown in Figure 1. The body 4 contains, in addition to the arrangement of the thermocouple employed to measure horizontal temperature gradient. a cylinder of metal 23 arranged in its upper end. This metal has a high heat capacity and is insulated from the borehole fluid by body 6. One junction 26 of a thermocouple is embedded in this cylinder of metal. The other junction of this thermocoupie is exposed at the lower end of the body 6 to be secured by Letters Patent is:

1. A method for determining the nature of substrate traversed by a borehole filled with a fluid which comprises measuring the horizontal temperature gradient between the center and the I wall of the borehole at successive points along the borehole.

2. An apparatus for making measurements in a'borehole comprising abody adapted to be lowered into the-borehole, said body having a portion adapted to traverse the borehole adjacent the walls thereof and a portion adapted to traverse the center of said borehole,

thermocouple junctions exposed on each of said portions and means adapted to be located at the surface and electrically connected to said junctions to record a value indicative of the temperature difference between them. v

- 3. Anapparatus for making temperature measurements in a bore hole comprising a body adapted to be lowered into the bore hole, said body having a portion adapted to traverse the bore hole adjacent the walls thereof and a portion adapted to traverse the center of said bore hole, thermocouple junctions exposed on each of said-portions and positioned in the same horiaontal plane in said apparatus, and means-adapted to be located at the surface and electrically connected to said junctions to record a value indicative of the temperature diflerence between mmwm w. BLAU.- anoaen- E. CANNON.

temperature 

